Semiconductor device producing method

ABSTRACT

In a method for producing a semiconductor device having a through electrode structure, a masking material is formed so as to bridge over a through hole formed in a second semiconductor substrate, and a hole is formed in the masking material at a position corresponding to the through hole. A contact hole is formed in an insulating film via this hole. In such a method, even if there is a large level difference from the surface of the second semiconductor substrate to the bottom of the through hole, only the masking material bridged over the through hole is exposed by photolithography. Therefore, photolithography for a large level difference is not necessary. As a result, the hole can be formed in the masking material successfully, and the contact hole can be formed successively by an anisotropic dry etching via this hole, even in the case where etching for a large level difference is performed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Applications No.2012-195191 filed on Sep. 5, 2012 and No. 2013-127545 filed on Jun. 18,2013, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device producingmethod for forming a through electrode structure in a semiconductorsubstrate.

BACKGROUND ART

Conventionally, a multi-layer structure made by bonding twosemiconductor substrates has been used for the purposes of highfunctionalization of a semiconductor chip and protection of an elementforming a sensor with a MEMS (micro electro mechanical systems)structure from an external environment. In a semiconductor device havingsuch a structure, a through electrode structure is used to make electricconduction between the substrates, and to lead out a potential of eachpart formed inside of the bonded semiconductor substrates. To form sucha through electrode structure, for example, a method indicated in apatent literature 1 is generally used.

As a method for forming the through electrode structure, for example, athrough hole is formed in one of the semiconductor substrates and aninsulating film is formed on a periphery or the like of the through holeby a thermal oxidation process, before the two semiconductor substratesare bonded to each other. Thereafter, the semiconductor substrate inwhich the through hole has been coated with the insulating film isbonded to a support substrate, and then the through hole is filled witha metal by a plating process. Further, the semiconductor substrate isseparated from the support substrate, and then is bonded to the other ofthe semiconductor substrates. In this way, the through hole is formed inone of the semiconductor substrates, and is filled with the metal.Thereafter, the one of the semiconductor substrates is bonded to theother of the semiconductor substrates. As a result, the throughelectrode structure is formed.

PRIOR ART LITERATURE Patent Literature

Patent Literature 1: Japanese Patent No. 3751625 B2.

SUMMARY OF INVENTION

In a case where the through electrode structure is formed by the methodindicated by the patent literature 1, since the support substrate isused, a production process is complicated. Also, since various steps areperformed before the substrates are bonded, the surface of the substrateis roughed or the substrate is deformed. As a result, a bonding qualityis affected. For example, the surface of the substrate is roughed due toan influence caused by separation from the support substrate, or thelike. The deformation of the substrate is, for example, caused by adifference of coefficient of expansion between the metal filled in thethrough hole or the inside and the semiconductor substrate.

Therefore, in the semiconductor device with the multi-layer structure,it is preferable to form the through electrode after the twosemiconductor substrates are bonded to each other. In such a case,however, it is necessary to form a contact hole in an insulating filmlocated at a bottom of the through hole from a front surface side of thesubstrate, and to pattern a wiring pattern while protecting a metal filminside of the through hole. That is, it is necessary to performphotolithography and etching steps with a large level difference, whichis difficult to realize. Therefore, it is desired to properly realizethe large level difference photolithography and etching process.

As an example of a case that requires the large level differencephotolithography and etching process, the through electrode structure ofthe multi-layer semiconductor device made of the two bondedsemiconductor substrates has been mentioned above. The large leveldifference photolithography and etching process may be required also inother cases. That is, the large level difference photolithography andetching process is required in a case of etching a thin film disposedinside of a recessed portion formed adjacent to a surface of asemiconductor substrate, at a predetermined position of the bottom ofthe recessed portion. It is desired to successfully realize the largelevel difference photolithography and etching process.

Considering the foregoing issues, it is a first object of the presentdisclosure to provide a semiconductor device producing method, which iscapable of successfully realizing a large level differencephotolithography and etching process to etch a predetermined position ata bottom of a recessed portion that is formed adjacent to a surface of asemiconductor substrate. It is a second object of the present disclosureto provide a semiconductor device producing method, which is capable offorming a through electrode structure by successfully performing a highlevel difference etching, while restricting an occurrence of a roughsurface or deformation of a substrate before bonding substrates, andwithout requiring a support substrate.

According to an aspect of the present disclosure, a semiconductor deviceproducing method includes: preparing a semiconductor substrate formedwith a recessed portion adjacent to a surface of the semiconductorsubstrate; forming a thin film on an inner wall surface of the recessedportion; arranging a masking material on the thin film so that themasking material bridges over the recessed portion while remaining aninside of the recessed portion as a cavity, after the forming of thethin film; forming a hole in the masking material at a positioncorresponding to the recessed portion; and performing a processing ofremoving the thin film at the position corresponding to the hole throughthe hole by an anisotropic dry etching using the masking material.

As described above, the masking material is formed to bridge over therecessed portion, and the hole is formed in the masking material at theposition corresponding to the recessed portion. Further, the thin filmis etched through this hole. In such a producing method, even if thereis a large level difference from the surface of the semiconductorsubstrate to the bottom of the recessed portion, only the maskingmaterial, which is bridged over the recessed portion, is exposed by thephotolithography, and it is not necessary to perform a photolithographythrough a large level difference. Therefore, the hole can besuccessfully formed in the masking material. In addition, even in theetching through the large level difference, the contact hole can besuccessfully formed by the anisotropic dry etching through the hole. Assuch, the large level difference photolithography and etching process,which is difficult to realize, can be successfully realized.

According to a second aspect of the present disclosure, a semiconductordevice producing method includes: preparing a first semiconductorsubstrate formed with an element and a connection portion; bonding asecond semiconductor substrate to a surface of the first semiconductorsubstrate; forming a through hole in the second semiconductor substrateafter being bonded to the first semiconductor substrate by etching thesecond substrate at a position corresponding to the connection portionfrom a surface opposite to the first semiconductor substrate; forming aninsulating film on the surface of the second semiconductor substrateincluding an inner wall surface of the through hole and the connectionportion exposed inside of the through hole; arranging a first maskingmaterial on the insulating film so that the first masking materialbridges over the through hole while remaining an inside of the throughhole as a cavity, after the forming of the insulating film; forming ahole in the first masking material at a position corresponding to thethrough hole; and forming a contact hole to expose the connectionportion for contacting the connection portion with a conductive layer byremoving the insulating film at a position corresponding to the holethrough the hole by an anisotropic dry etching using the first maskingmaterial.

As described above, the first masking material is formed to bridge overthe through hole, and the hole is formed in the first masking materialat the position corresponding to the through hole. The contact hole isformed in the insulating film through the hole. In such a producingmethod, even if there is a large level difference from the surface ofthe second semiconductor substrate to the bottom of the through hole,only the first masking material bridged over the through hole is exposedby the photolithography, and a photolithography with a large leveldifference is not necessary. As such, the hole can be successfullyformed in the masking material, and the contact hole can be successfullyformed even by the etching with the large level difference by theanisotropic dry etching through the hole. Accordingly, the large leveldifference photolithography and etching process, which is difficult torealize, can be successfully realized.

As such, the through electrode structure is successfully formed. In sucha semiconductor device producing method, further, the firstsemiconductor substrate and the second semiconductor substrate arebonded to each other before the through hole is formed. Therefore, it isnot necessary to use the support substrate as a conventional method.Also, it is less likely that the surface of the substrate will beroughed and the substrate will be deformed. Accordingly, the throughelectrode structure can be formed by successfully performing the largelevel difference etching without requiring the support substrate andrestricting the occurrence of the rough surface and the deformation ofthe substrate.

According to a third aspect of the present disclosure, in the forming ofthe hole in the semiconductor device producing method according to thesecond aspect, the hole has a diameter smaller than a diameter of thethrough hole.

In such a hole, a normal line of the second semiconductor substratepassing through the hole does not pass through a portion of theinsulating film formed on a side wall surface of the through hole.Therefore, in the anisotropic dry etching, only a portion of theinsulating film disposed on the bottom of the through hole can beremoved without damaging the side wall of the through hole.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings, in which:

[FIG. 1] FIG. 1 is an enlarged cross-sectional view of a throughelectrode structure of a semiconductor device that is produced by asemiconductor device producing method according to a first embodiment ofthe present disclosure;

[FIG. 2](a) to (d) of FIG. 2 are cross-sectional views illustrating aproducing process of the through electrode structure of thesemiconductor device shown in FIG. 1;

[FIG. 3](a) to (d) of FIG. 3 are cross-sectional views illustrating aproducing process subsequent to the producing process shown in (a) to(d) of FIG. 2;

[FIG. 4](a) to (d) of FIG. 4 are cross-sectional views illustrating aproducing process subsequent to the producing process shown in (a) to(d) of

FIG. 3;

[FIG. 5] FIG. 5 is an enlarged view of a part in the vicinity of acontact hole 5 a;

[FIG. 6] FIG. 6 is a cross-sectional view illustrating relationships ofdimensions of respective parts of a through hole 3 a and dimensions ofrespective parts of a masking material 10; and

[FIG. 7](a) to (d) of FIG. 7 are cross-sectional views illustrating aproducing process of an etching processing part of a semiconductordevice that is produced by a semiconductor device producing methodaccording to another embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. The embodiments are describedhereinafter by designating the same or equivalent parts with the samereference numbers.

First Embodiment

A first embodiment of the present disclosure will be described.Hereinafter, of a semiconductor device made by bonding two semiconductorsubstrates, only a part associated with a through electrode structurewill be described. However, the semiconductor device is actuallyprovided with other elements. The present disclosure can be applied tovarious semiconductor devices provided with such a through electrodestructure. For example, the present disclosure can be applied to asemiconductor device in which a semiconductor substrate forming a wiringpattern is bonded to a semiconductor substrate formed with an integratedcircuit. Also, the present disclosure can be applied to a semiconductordevice in which a semiconductor substrate forming a cap is bonded to afront surface of a semiconductor substrate formed with a sensor with aMEMS structure such as an acceleration sensor.

Referring to FIG. 1, a through electrode structure of a semiconductordevice produced by a semiconductor producing method according to thepresent embodiment will be firstly described.

As shown in FIG. 1, a first semiconductor substrate 1 is formed with anintegrated circuit and a sensor having a MEMS structure, and a secondsemiconductor substrate 3 is bonded to a front surface of the firstsemiconductor substrate 1 through an insulating film 2 made of anoxidation film or the like. For example, the first semiconductorsubstrate 1 and the second semiconductor substrate 3 are made of siliconsubstrate.

A connection portion 4 is formed on the front surface of the firstsemiconductor substrate 1, and the connection portion 4 is exposed froma contact hole 2 a of the insulating film 2, which is formed at aposition corresponding to the connection portion 4. The connectionportion 4 is a portion to be electrically connected to a desiredposition of the first semiconductor substrate 1. For example, in a casewhere the first semiconductor substrate 1 is provided with an integratedcircuit or the like, the connection portion 4 is provided as a pad thatconnects to a wiring pattern extending from the integrated circuit onthe front surface of the first semiconductor substrate 1. For example,in a case where the first semiconductor substrate 1 is provided with asensor having a MEMS structure, the connection portion 4 is provided asa diffusion layer that makes electrical connection with each part of theMEMS structure. In a case where the sensor is an acceleration sensorhaving a movable electrode and a fixed electrode, the connection portion4 is electrically connected to the fixed electrode or the movableelectrode. The diffusion layer or the like is generally electricallyconnected when being extended to each part of the MEMS structure.Alternatively, there is a case where the first semiconductor substrate 1doped with impurities is used as a wiring. In such a case, theconnection portion 4 made of the diffusion layer is connected to eachpart of the MEMS structure through the first semiconductor substrate 1.

The second semiconductor substrate 3 is formed with a through hole 3 aat a position corresponding to the connection portion 4. The throughhole 3 a penetrates through the second semiconductor substrate 3 from afront surface to a rear surface. The contact hole 2 a formed in theinsulating film 2 described above is formed at a position correspondingto the through hole 3 a.

A front surface of the second semiconductor substrate 3, including aninner wall surface of the through hole 3 a, and an exposed surface ofthe connection portion 4 are covered with an insulating film 5. Theinsulating film 5 is also formed with a contact hole 5 a at a positioncorresponding to the connection portion 4. Therefore, the connectionportion 4 is exposed also from the insulating film 5 through the contacthole 5 a within the through hole 3 a.

A conductive layer 6, which is made of a metal, is patterned on thesurface of the insulating film 5 including the inside of the throughhole 3 a and the inside of the contact hole 5 a. Since the conductivelayer 6 contacts the connection portion 4 though the contact hole 5 a,the electric connection from the front surface of the secondsemiconductor substrate 3 to the connection portion 4 is implementedthrough the conductive layer 6. Therefore, the potential of theconnection portion 4 provided in the first semiconductor substrate 1 canbe taken out from the front surface of the second semiconductorsubstrate 3 opposite to the first semiconductor substrate 1 through thethrough hole 3 a and the contact holes 2 a and 5 a.

In addition, a passivation film 7 is formed to cover a surface of theconductive layer 6, if necessary. Thus, the conductive layer 6 andelements formed in the first semiconductor substrate 1 can be protected.In such a case, the passivation film 7 is removed at a desired positionto expose the conductive layer 6, and the potential of the connectionportion 4 can be taken out from the exposed portion as a pad.

Next, a producing method of the semiconductor device configured asdescribed above will be described with reference to (a) of FIG. 2through (d) of FIG. 4. It is to be noted that the semiconductor deviceis actually provided with other elements and the like, though only thepart of the through electrode structure is illustrated.

[Step Shown in (a) of FIG. 2]

Firstly, a first semiconductor substrate 1 in which an integratedcircuit, elements such as sensors with the MEMS structure, and theconnection portion 4 are formed by a conventional method is prepared.Also, a second semiconductor substrate 3 is prepared. The insulatingfilm 2 is formed on a rear surface of the second semiconductor substrate3, that is, on a surface of the second semiconductor substrate 3 that isto be bonded to the first semiconductor substrate 1. For example, theinsulating layer 2 is formed on the rear surface of the secondsemiconductor substrate 3 by forming an oxide film by thermal oxidationor the like. Then, the second semiconductor substrate 3 is placed on thefront surface of the first semiconductor substrate 1, that is, on thesurface of the first semiconductor substrate 1 on which the connectionportion 4 has been formed. The first semiconductor substrate 1 and thesecond semiconductor substrate 3 are bonded to each other through theinsulating film 2, such as by direct bonding. Further, the secondsemiconductor substrate 3 is grinded and polished from the frontsurface, if necessary, to adjust the thickness suitable for formation ofthe through electrode structure. For example, it is preferable to setthe thickness of the second semiconductor substrate 3 in a range fromseveral tens pm to approximately 200 μm (for example, 100 μm).

[Step Shown in (b) of FIG. 2]

An etching mask (not shown) is arranged on the front surface of thesecond semiconductor substrate 3. The etching mask is formed with anopening at a position corresponding to a region where the through hole 3a is to be formed. Then, etching is carried out for the secondsemiconductor substrate 3 using the etching mask, so that the throughhole 3 a, which penetrates through the second semiconductor substrate 3from the front surface to the rear surface, is formed in the secondsemiconductor substrate 3 and the contact hole 2 a is formed in theinsulating film 2. The through hole 3 a may be formed such that a sidewall surface of the through hole 3 a is perpendicular to the frontsurface of the second semiconductor substrate 3. However, the throughhole 3 a is preferably formed into a forward taper shape in which anarea of opening gradually reduces from the front surface toward the rearsurface of the second semiconductor substrate 3. In the case where thethrough hole 3 a is formed into such a forward taper shape, theinsulating film 5 and the conductive layer 6 are favorably attached tothe side wall surface of the through hole 3 a when the insulating film 5and the conductive layer 6 are formed in the through hole 3 a in latersteps.

Although the method of forming the through hole 3 a into the forwardtaper shape has been conventionally known and thus a detail descriptionthereof will be omitted, the through hole 3 a having the forward tapershape can be easily formed only by setting an etching condition. Forexample, it is preferable that a diameter of the through hole 3 a on thefront surface of the second semiconductor substrate 3 is set to a rangefrom approximately 50 μm to approximately 150 μm, and a taper angle,which is an angle defined between the rear surface of the secondsemiconductor substrate 3 and the inner wall surface of the through hole3 a, is in a range from 70 to 80°.

[Step Shown in (c) of FIG. 2]

The insulating film 5 is formed on the front surface of the secondsemiconductor substrate 3, including the inner wall surface of thethrough hole 3 a and the surface of the connection portion 4 exposedfrom the through hole 3 a, by a CVD technique, a thermal oxidation, andthe like. Even in the case of employing the CVD technique, when theinner wall surface of the through hole 3 a has the forward taper shapeas described above, the insulating film 5 can be formed on and properlyattached also to the inner wall surface of the through hole 3 a.

[Step Shown in (d) of FIG. 2]

A masking material 10 (a first masking material) is formed by carryingout a film-formation of a tenting method to the front surface of thesecond semiconductor substrate 3, by a spin coating of a photoresist, adry film attachment, or the like. In this case, the masking material 10is bridged over the through hole 3 a while remaining the inside of thethrough hole 3 a as a cavity and is configured to cover the insulatingfilm 5 and the second semiconductor substrate 3 as base materials.Further, through a photolithography step, a hole 10 a having a diametersmaller than a diameter of the through hole 3 a is formed in the maskingmaterial 10 at a position corresponding to the through hole 3 a. Thediameter of the hole 10 a is, for example, approximately 20 to 50 μm.Although the thickness of the masking material 10 is arbitrary, thethickness of the masking material 10 is adjusted so that a thermalexpansion of gas in the cavity of the through hole 3 a can be suppressedduring baking before exposure in the photolithography step.

As a resist material for forming the masking material 10, for example,PMER P-CT700XP (brand name) made by TOKYO OHKA KOGYO., LTD. can be used.Further, if necessary, an additive is mixed to the resist material toincrease a surface tension of the resist material. When a low-speed spincoating or the like is performed in a state where the surface tension ofthe resist material is increased by the additive, the masking material10 can be formed into a tenting shape without falling down into thethrough hole 3 a.

[Step Shown in (a) of FIG. 3]

A part of the insulating film 5 is removed by an anisotropic dry etchingusing the masking material 10 to form the contact hole 5 a in theinsulating film 5 at a position to which the hole 10 a is projected in adirection of normal to the substrate. In such an etching, a normal lineof the second semiconductor substrate 2 passing through the hole 10 adoes not pass through the portion of the insulating film 5 formed on theside wall surface of the through hole 3 a. Therefore, only the portionof the insulating film 5 located on the bottom of the through hole 3 acan be removed without damaging the side wall of the through hole 3 a.When the contact hole 5 a is formed in this manner, a side wall surfaceof the contact hole 5 a has a rounded shape, as shown in an enlargedcross-section of FIG. 5. Therefore, it is possible to improve a fillingproperty (coverage property) of the conductive layer 6, which is formedin a later step, in the contact hole 5 a.

[Steps Shown in (b) and (c) of FIG. 3]

As shown in (b) of FIG. 3, the masking material 10 is removed.Thereafter, as shown in (c) of FIG. 3, the conductive layer 6 made of ametal is formed on an entire surface of the insulating film 5 includingthe inside of the contact hole 5 a. For example, the conductive layer 6is formed by a sputtering or a CVD technique.

[Step Shown in (d) of FIG. 3]

Similarly to the masking material 10, a masking material 11 (secondmasking material) is formed by a tenting method. Also in this case, themasking material 10 is formed to bridge over the through hole 3 a whileremaining the inside of the through hole 3 a as a cavity and to coverthe conductive layer 6 and the second semiconductor substrate 3 as basematerials, including the inside of the through hole 3 a. Through aphotolithography step, the portion of the masking material 11corresponding to an unnecessary portion of the conductive layer 6 isremoved to form an opening.

[Step Shown in (a) of FIG. 4]

The conductive layer 6 is patterned by partly removing the conductivelayer 6 through the etching using the masking material 11. In such anetching, since the masking material 11 covers the through hole 3 a, theconductive layer 6 can be removed without damaging the side wall of thethrough hole 3 a.

[Steps Shown in (b) and (c) of FIG. 4]

As shown in (b) of FIG. 4, the masking material 11 is removed.Thereafter, as shown in (c) of FIG. 4, a passivation film 7, such as anitride film, is formed to cover an entire surface of the conductivelayer 6 including the inside of the through hole 3 a. For example, thepassivation film 7 is formed by a spin coating technique.

[Step Shown in (d) of FIG. 4]

Similarly to the masking materials 10 and 11, a masking material 12(third masking material) is formed again by a tenting method. Also inthis case, the masking material 12 is formed to bridge over the throughhole 13 a while remaining the inside of the through hole 3 a as a cavityand to cover the conductive layer 6 as the base material including theinside of the through hole 3 a. Through a photolithography step, aportion of the masking material 12 corresponding to an unnecessaryportion of the passivation layer 7 is removed to form an opening.Thereafter, the unnecessary portion of the passivation film 7 is removedby an etching using the masking material 12, and then the maskingmaterial 12 is removed. As such, the semiconductor device having thethrough electrode structure shown in FIG. 1 is finished.

In the present embodiment, as described above, the masking material 10is formed to bridge over the through hole 3 a, and the hole 10 a isformed in the masking material 10 at the position corresponding to thethrough hole 3 a. The contact hole 5 a is formed in the insulating film5 through the hole 10 a. In such a producing method, even if there is alarge level difference between the front surface of the secondsemiconductor substrate 3 and the bottom of the through hole 3 a, onlythe masking material 10 bridged over the through hole 3 a is exposed inthe photolithography step. Further, a photolithography step with a largelevel difference is not necessary. Therefore, the hole 10 a issuccessfully formed in the masking material 10. In addition, even in theetching with the large level difference, the contact hole 5 a issuccessfully formed by the anisotropic dry etching through the hole 10a. Therefore, a large level difference photolithography and etchingprocess (photolithography step and large level difference etching step),which is difficult to realize, can be successfully realized.

Also in the patterning of the conductive layer 6 and the passivationfilm 7, the masking materials 11 and 12 are similarly bridged over thethrough hole 3 a. Therefore, even if there is a large level differencefrom the surface of the conductive layer 6 and the passivation film 7 tothe bottom of the through hole 3 a, only the masking materials 11 and 12bridged over the through hole 3 a are exposed by the photolithographystep, and there is no large level difference. Therefore, similarly tothe above, the large level difference photolithography and etchingprocess, which is difficult to realize, can be successfully realized.

Therefore, the through electrode structure can be successfully formed.In such a producing method of the semiconductor device, the firstsemiconductor substrate 1 and the second semiconductor substrate 3 arebonded to each other before the through hole 3 a is formed. Therefore,it is not necessary to use the support substrate, as a conventionalmethod. Also, occurrence of the rough surface of the substrate ordeformation of the substrate before the bonding of the substrates can bereduced. Accordingly, the occurrences of the rough surface of thesubstrate and the deformation of the substrate before the bonding of thesubstrates can be reduced without requiring the support substrate, andthe through electrode structure can be formed by successfully performingthe large level difference etching.

The diameter of the through hole 3 a, the taper angle defined betweenthe rear surface of the second semiconductor substrate 3 and the innerwall surface of the through hole 3 a, the diameter of the hole 10 a ofthe masking material 10, and the thickness of the second semiconductorsubstrate 3 to which the through hole 3 a is formed, that is, the depthof the through hole 3 a are set to the values as described above. Thereasons thereof will be described with reference to FIG. 6.

As described above, because the diameter of the hole 10 a is smallerthan the diameter of the through hole 3 a, the normal line of the secondsemiconductor substrate 3 passing through the hole 10 a does not passthrough the portion of the insulating film 5 formed on the side wallsurface of the through hole 3 a. Therefore, the side wall of the throughhole 3 a is not damaged during the etching. However, as described withreference to FIG. 5, when the contact hole 5 a is formed by removing theportion of the insulating film 5, the side wall surface of the contacthole 5 a actually has the rounded shape. The side wall surface of thecontact hole 5 a has the rounded shape because the cavity remains in thethrough hole 3 a by arranging the masking material 10 in the tentingshape and the etching for forming the contact hole 5 a is performedwhile expanding in a radial direction, as shown in FIG. 6.

Since the etching is performed while expanding in the radial direction,the filling property of the conductive layer 6 in the contact hole 5 acan be improved. On the contrary, since the etching is performed whileexpanding in the radial direction, if the diameter of the through hole 3a is excessively small or depending on the taper angle of the throughhole 3 a, the insulating film 5 formed on the side surface of thethrough hole 3 a is also etched. Therefore, the diameter of the throughhole 3 a, the diameter of the hole 10 a of the masking material 10 andthe taper angle of the through hole 3 a need to be set so as to avoidetching the insulating film 5 formed on the side wall surface of thethrough hole 3 a. The diameter of the through hole 3 a and the diameterof the hole 10 a can be obtained in the following manner.

First, the diameter of the through hole 3 a on an opening side (diameteron the front surface opposite to the first semiconductor substrate 1) isreferred to as L1. The diameter of the through hole 3 a on the surfaceadjacent to the first semiconductor substrate 1 is referred to as L2.The diameter of the hole 10 a is referred to as L3. The taper angle ofthe through hole 3 a is referred to as a, and an expanding angle of theetching is referred to as β. The depth of the through hole 3 a, that is,the thickness of the second semiconductor substrate 3 in the case of thepresent embodiment, is referred to as D1. A distance from the surface ofthe insulating film 5 on the outside of the through hole 3 a to thesurface of the second semiconductor substrate 3 adjacent to the firstsemiconductor substrate 1 is referred to as D2.

In this case, the depth D1 of the through hole 3 a can be expressed byan equation 1. Also, the diameter L2 of the through hole 3 a adjacent tothe first semiconductor substrate 1 in the equation 1 can be expressedby an equation 2.

D1=(L1−L2)/2 tan α  (Ex. 1)

L2=L1−2D1/tan α  (Ex. 2)

The etching diameter of the insulating film 5 at the end of the throughhole 3 a adjacent to the first semiconductor substrate 1 needs to besmaller than the diameter L2 of the through hole 3 a adjacent to thefirst semiconductor substrate 1. Therefore, an equation 3 is given.Further, since the distance D2 is substantially equal to the thicknessD1 of the second semiconductor substrate 3 (D1≈D2), the D2 can bereplaced with the D1.

L2≧L3+2D2 tan β(≈L3+2D1 tan β)   (Ex. 2)

The expanding angle β of the etching is a constant determined accordingto the etching condition and the like. Therefore, when the depth D1 ofthe through hole 3 a and the diameters L1 to L3 are set whileconsidering the expanding angle β determined according to the etchingcondition and satisfying the above described equations 1 to 3, it ispossible to restrict the insulating film 5 formed on the side wallsurface of the through hole 3 a from being etched.

When the diameter L1 on the opening side of the through hole 3 a and thediameter L2 of the through hole 3 a adjacent to the first semiconductorsubstrate 1 are large, the effects described above can be achieved.However, if the diameter L1 of the though hole 3 a on the opening sideis excessively large, there is a problem arise, such as a part of themasking material 10 entering the through hole 3 a when being bridgedover the through hole 3 a. Likewise, when the diameter L1 of the throughhole 3 a on the opening side is excessively large, it is difficult tosuppress the thermal expansion of gas in the cavity defined in thethrough hole 3 a during the baking before the exposure. The upper limitof the diameter L1 of the through hole 3 a on the opening side ispreferably set considering these issues.

Each value is preferably set in the above described manner. For example,when the thickness of the second semiconductor substrate 3, that is, thedepth D1 of the through hole 3 a is several tens to 200 μm, as describedabove, it is preferable that the diameter L1 of the through hole 3 a onthe opening side is 50 to 150 μm, and the taper angle a is 70 to 80°,and the diameter L3 of the hole 10 a is 20 to 50 μm.

Other Embodiments

In the embodiment described above, the structure in which the conductivelayer 6 is extended on the front surface of the second semiconductorsubstrate 3, for example, the mode in which the conductive layer 6 formsthe wiring pattern is indicated, as shown in FIG. 1. However, it may beconfigured that the conductive layer 6 is remained only on the peripheryof the through hole 3 a to form a pad.

In the embodiment described above, as an example of the semiconductordevice, the semiconductor device provided with the integrated circuitand the MEMS structure is mentioned. However, the above semiconductordevice is just an example, and the semiconductor device may be providedwith any other elements. The semiconductor device may have any structureas long as the semiconductor device is provided by bonding the firstsemiconductor substrate 1 and the second semiconductor substrate 3 toeach other, and the potential of the connection portion 4 of the firstsemiconductor substrate 3 is led out through the through hole 3 a thatpenetrates through the second semiconductor substrate 3 from the frontsurface toward the first semiconductor substrate 1.

In the embodiment described above, as an example of requiring the largelevel difference photolithography and etching process, the throughelectrode structure in the multi-layer structure semiconductor substrateprovided by the first and second semiconductor substrate 1 and 3 bondedto each other is mentioned. That is, in the structure where the twosemiconductor substrates 1 and 3 are bonded to each other through theinsulating film 2 to form an integrated semiconductor substrate, and arecessed portion provided by the through hole 3 a is formed on one sideof the integrated semiconductor substrate (adjacent to the secondsemiconductor substrate 3), the insulating film 5 as a thin film isexemplarily provided in the recessed portion. However, the large leveldifference photolithography and etching process may be also required inother cases.

Namely, in a case where a semiconductor substrate having a recessedportion adjacent to a surface is prepared, and a step of etching isperformed to a predetermined portion of a bottom part of a thin filmdisposed in the recessed portion, the large level differencephotolithography and etching process is required. Also in this case, thesimilar effects to the first embodiment can be achieved by performingthe following steps subsequently. First, as shown in (a) of FIG. 7, asemiconductor substrate 20 is prepared. Then, as shown in (b) of FIG. 7,a step of forming a recessed portion 20 a on a surface of thesemiconductor substrate 20 is performed. Next, as shown in (c) of FIG.7, a step of forming a thin film 21 on an inner wall surface of therecessed portion 20 a is performed. Thereafter, as shown in (d) of FIG.7, a step of arranging a masking material 22 on the thin film 21 tobridge over the recessed portion 20 a is performed. Further, a step offorming a hole 22 a in the masking material 22 at a positioncorresponding to the recessed portion 20 a is performed by aphotolithography. Thereafter, a step of removing the thin film 21 at aposition corresponding to the hole 22 a is performed through the hole 22a by an anisotropic dry etching through the hole 22 a. In this way, thethin film 21 can be etched on the bottom wall of the recessed portion 20a. The large level difference photolithography and etching process,which is difficult to realize, can be successfully realized.

While only the selected exemplary embodiment and examples have beenchosen to illustrate the present disclosure, it will be apparent tothose skilled in the art from this disclosure that various changes andmodifications can be made therein without departing from the scope ofthe disclosure as defined in the appended claims. Furthermore, theforegoing description of the exemplary embodiment and examples accordingto the present disclosure is provided for illustration only, and not forthe purpose of limiting the disclosure as defined by the appended claimsand their equivalents.

1. A producing method for a semiconductor device, comprising: preparinga semiconductor substrate formed with a recessed portion adjacent to asurface of the semiconductor substrate; forming a thin film on an innerwall surface of the recessed portion; after the forming of the thinfilm, arranging a masking material on the thin film so that the maskingmaterial bridges over the recessed portion while remaining an inside ofthe recessed portion as a cavity; forming a hole in the masking materialat a position corresponding to the recessed portion by photolithography;and performing a processing of removing the thin film at a positioncorresponding to the hole through the hole by an anisotropic dry etchingusing the masking material.
 2. A producing method for a semiconductordevice, the semiconductor device having: a first semiconductor substratehaving a connection portion adjacent to a surface of the firstsemiconductor substrate to be connected to an element; and a secondsemiconductor substrate bonded to the surface of the first semiconductorsubstrate, wherein the second semiconductor substrate includes a throughelectrode structure having a through hole formed in the secondsemiconductor substrate from a front surface opposite to the firstsemiconductor substrate and a conductive layer disposed in the throughhole and connected to the connection portion, the producing methodcomprising: preparing the first semiconductor substrate formed with theelement and the connection portion; bonding the second semiconductorsubstrate to the surface of the first semiconductor substrate; after thebonding of the second semiconductor substrate to the surface of thefirst semiconductor substrate, forming the through hole by etching thesecond semiconductor substrate from the front surface opposite to thefirst semiconductor substrate at a position corresponding to theconnection portion of the second semiconductor substrate; forming aninsulating film on the front surface of the second semiconductorsubstrate, including an inner wall surface of the through hole and theconnection portion exposed from the through hole; after the forming ofthe insulating film, arranging a first masking material on theinsulating film so that the first masking material bridges over thethrough hole while remaining an inside of the through hole as a cavity;forming a hole in the first masking material at a position correspondingto the through hole by photolithography; and forming a contact hole inthe insulating film to expose the connection portion for contacting theconnection portion with the conductive layer, by removing the insulatingfilm at a position corresponding to the hole through the hole by ananisotropic dry etching using the first masking material.
 3. Theproducing method according to claim 2, wherein in the forming of thehole, the hole is formed to have a diameter smaller than a diameter ofthe through hole.
 4. The producing method according to claim 2, whereinin the forming of the through hole, the through hole is formed into aforward tapered shape such that an area of opening of the through holegradually reduces as a function of distance from the front surface ofthe second semiconductor substrate opposite to the first semiconductorsubstrate.
 5. The producing method according to claim 2, comprisingafter the forming of the contact hole, contacting the conductive layerwith the connection potion through the contact hole by forming theconductive layer on a surface of the insulating film including an insideof the contact hole.
 6. The producing method according to claim 5,further comprising: after the forming of the conductive layer, arranginga second masking material on the conductive layer so that the secondmasking material bridges over the through hole while remaining theinside of the through hole as a cavity; forming an opening in the secondmasking material at a position corresponding to an unnecessary portionof the conducive layer by photolithography; and patterning theconductive layer by removing the unnecessary portion of the conductivelayer by etching using the second masking material.
 7. The producingmethod according to claim 6, further comprising: after the patterning ofthe conductive layer, forming a passivation film on the conductivelayer; after the forming of the passivation film, arranging a thirdmasking material on the passivation film so that the third maskingmaterial bridges over the through hole while remaining the inside of thethrough hole as a cavity; forming an opening in the third maskingmaterial at a position corresponding to an unnecessary portion of thepassivation film; and patterning the passivation film by removing theunnecessary portion of the passivation film by etching using the thirdmasking material.
 8. A producing method for a semiconductor device,comprising: preparing a first semiconductor substrate having an elementand a connection portion; bonding a second semiconductor substrate to asurface of the first semiconductor substrate; after the bonding of thesecond semiconductor substrate, forming a through hole by etching thesecond semiconductor substrate from a front surface of the secondsemiconductor substrate opposite to the first semiconductor substrate ata position corresponding to the connection portion; forming aninsulating on an inner wall surface of the through hole, the connectionportion exposed from the through hole, and the front surface of thesecond semiconductor substrate; after the forming of the insulatingfilm, arranging a masking material on the insulating film so that themasking material bridges over the through hole while remaining an insideof the through hole as a cavity; forming a hole in the masking materialat a position corresponding to the through hole by photolithography; andforming a contact hole in the insulating film to expose the connectionportion by removing the insulating film at a position corresponding tothe hole through the hole by an anisotropic dry etching using themasking material.
 9. The producing method according to claim 8,comprising after the forming of the contact hole, contacting aconductive layer to the connection portion through the contact hole byforming the conductive layer on a surface of the insulating filmincluding an inside of the contact hole.